1. Field of the invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a dry etching method and apparatus for use in the LCD device.
2. Description of Related Art
FIG. 1 is a schematic view illustrating a typical liquid crystal display substrates 7 and 22 with a liquid crystal layer having liquid crystal molecules 15 interposed therebetween. The first substrate 7 as an upper substrate includes a color filter 5 and a transparent common electrode 9 formed on the color filter 5. The second substrate 22 as a lower substrate includes pixel regions “P”, pixel electrodes 18 formed on the pixel regions “P”, gate lines 21 arranged in a transverse direction, data lines 26 arranged in a perpendicular direction to the gate lines 21, and thin film transistors (TFTs) “T” arranged near the cross points of the gate and data lines 21 and 26.
Each TFT includes an active layer, a gate electrode, and source and drain electrodes. The gate electrode contacts the gate line 21 and the source electrode contacts the data lines 26. Also, the drain electrode contacts the pixel electrode 18.
Components of the TFT, for example the active layer, the gate, source and drain electrodes and the like, are formed using a deposition technique, a photolithography technique, and an etching technique.
The etching technique includes dry-etching and a wet-etching. The dry-etching also includes plasma dry-etching, ion beam milling etching, and reactive ion etching. In wet-etching, acids and other chemical solutions are used as an etchant. In chemical dry-etching, for example the plasma dry-etching, plasma is used to generate gas radicals such as fluorine radicals in order to etch any portions of a thin film that are not covered by a photoresist. In physical dry-etching, for example the ion beam milling etching, an ion beam is used in order to etch any portions of a thin film that are not covered by the photoresist.
FIG. 2 is a schematic view illustrating a conventional dry-etching apparatus. As shown in FIG. 2, the dry-etching apparatus includes a process chamber 41, a cathode electrode 43 as an upper electrode to which voltage is applied, an anode electrode 45 as a lower electrode facing the cathode electrode 43 and having an top layer 48 on a substrate 49, and a RF (radio frequency) generator 50 that generates RF power.
The dry-etching process will be explained in detail hereinafter in reference with FIG. 2.
First, in the plasma dry-etching, the substrate 49 including the top layer 48 that is a dry-etching member is placed on the lower electrode 45 in the process chamber 41, and the process chamber 41 being a vacuum environment due to a vacuum device (not shown). Sequentially, etching gas containing an etchant suitable for the top layer 48 is injected into the process chamber 41 for reaction with any portions of the top layer 48 that are not covered by the photoresist (not shown). Reactive energy required for the etchant to react with any portions of the top layer 48 that are not covered by the photoresist is supplied from a plasma 47 generated by the RF generator 50. Reactive energy generated by the plasma 47 excites the etching gas molecules to a high energy level so that the etching gas molecules react with any portions of the top layer 48 that are not covered by the photoresist. At this point, if the top layer 48 is made of SiO2, CF4 can be used as gas plasma. The gas plasma of CF4 reacts with SiO2 so that a gas containing fluorine, silicon, and oxygen is produced, thereby etching the SiO2 layer 48 arranged on the substrate 49. Thereafter, the gas of CF4 is removed from the chamber by evacuation.
Second, the ion beam milling etching uses an ion beam instead of the reactive energy of the chemical dry-etching to etch any portions of the top layer 48 that are not covered by the photoresist. The process chamber 41 remains in a vacuum atmosphere by a vacuum device (not shown). Sequentially, heated argon (Ar) gases are injected into the process chamber 41 and the RF generator 50 generates the RF power to produce Ar gas plasma, that is, Ar gases are ionized. And then, DC power is applied from a DC power source (not shown) to the upper and lower electrodes 43 and 45, and Ar cations (Ar+) are directed toward the lower electrode 45 and reacts with the top layer 48 on the substrate 49. Therefore any portions of the top layer 48 that are not covered by the photoresist are etched by ion beam confliction.
Finally, the reactive ion etching is a technique using both the chemical dry-etching such as the plasma etching, and the physical dry-etching such as the ion beam milling etching. Therefore, any portions of the top layer that are not covered by the photoresist are etched physically and chemically.
After the dry-etching process, a process of separating the substrate 49 from the lower electrode 45 follows. FIG. 3 is a perspective view illustrating an arrangement of the substrate 49 and the lower electrode 45. As shown in FIG. 3, the lower electrode 45 has a plurality of holes 51 receiving a plurality of lift pins 53 formed near two opposing end portions of the lower electrode 45. The lift pins 53 serve to lift the substrate 49 from the lower electrode 45 after the dry-etching process.
The substrate 49 is charged with electricity during the applying of RF power and, therefore capacitance is formed between the substrate 49 and the lower electrode 45 after the dry-etching, process. Furthermore, an electrostatic force or sucking force occurs between the substrate 49 and the lower electrode 45 due to the interaction between positive and negative charges. Consequently, as shown in FIG. 4A, when the lift pins 53 are raised, the substrate 49 is undesirably bent at the edges due to the electrostatic force between a center portion of the substrate 49 and the lower electrode 45. Even though the substrate 49 is separated from the lower electrode 45, the substrate 49 attached to the lower electrode 45 may pop up suddenly and be deformed by strong elasticity. As a result, as shown in FIG. 4B, the substrate 49 may even fall off the lift pins 53, causing damage to the substrate 49. Further, in case that the substrate 49 falls off the lift pins 53, a carrier arm that carries the substrate in a subsequent process 49 can not accurately receive the substrate 49, or may damage the substrate 49 during processing. In order to overcome the problems described above, an additional process that removes the electrical charges between the substrate 49 and the lower electrode 45 is necessary and thus requires a complex, lengthy process.